To repair an acrylic crack, you first have to drill a hole at the ends of the crack to prevent it from spreading further. Then you can weld a patch panel on both the inside and outside of the tank. Measure how long the crack is and that's how wide the patch needs to be, and it needs to extend 1/4 of the crack length past both ends of the crack. If the crack runs to an edge, your patch needs to be as flush as possible with the edge.
A repair of this nature is temporary at best and should only be done to buy you some time to set up a new tank. 50 gallons of water on your floor is nothing to play with, water damage can get expensive.